package cn.itcast.demo;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.IOException;

@WebServlet("/ServletDemo08")
public class ServletDemo08 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//          文件下载
//        1.创建字节输入流对象，关联读取的文件
//        获取文件绝对路径
        String realPath = getServletContext().getRealPath("/img/1.jpg");
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(realPath));
//        2.设置响应头支持的类型
        /*
            Content-type: 消息头名称  支持的类型
            application/octet-stream: 消息头参数  应用的类型为字节流
         */
        resp.setHeader("Content-type","application/octet-stream");

//        3.设置响应头以下载方式打开附件
        /*
            Content-Disposition: 消息头名称 处理形式
            attachment;filename=sign.png: 消息头参数  附件形式进行处理  指定文件下载名称

         */
            resp.setHeader("Content-Disposition","attachment;filename=sign.png");
//        4.获取字节输出流对象
        ServletOutputStream os = resp.getOutputStream();
//        5.循环读写
            byte[] bytes = new byte[1024];
            int len;
            while ((len = bis.read(bytes))!= -1){
                os.write(bytes,0,len);
            }
//        6.释放资源
            bis.close();




    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);
    }
}
